feat: parallelize device shutdown with common _shutdown_devices function

- Curfew and budget exhaustion now use shared _shutdown_devices()
- All device turnoffs run in parallel via ThreadPoolExecutor
- Faster shutdown when multiple devices need to be turned off

devices.py

@@ -258,7 +258,15 @@ def curfew_status() -> dict:
     }
 
 
-# ── Budget timer (runs every 60s in background) ──────────────────────
+def _shutdown_devices(device_ids: list[str]):
+    """Shut down a list of devices in parallel."""
+    if not device_ids:
+        return
+    with ThreadPoolExecutor(max_workers=len(device_ids)) as executor:
+        list(executor.submit(DEVICES[dev_id]["turnoff"]) for dev_id in device_ids)
+
+
+# ── Budget timer (runs every 10s in background) ──────────────────────
 
 _timer_running = False
 _timer_lock = threading.Lock()
@@ -292,13 +300,14 @@ def _budget_tick():
     # Process results sequentially (budget operations need to be thread-safe)
     with _timer_lock:
         if not is_curfew_allowed():
-            # Curfew in effect — turn off all online devices
-            for dev_id, online in online_status.items():
-                if online:
-                    DEVICES[dev_id]["turnoff"]()
+            # Curfew in effect — turn off all online devices in parallel
+            online_devices = [dev_id for dev_id, online in online_status.items() if online]
+            _shutdown_devices(online_devices)
             return
 
         current_time = time.time()  # float timestamp for precise elapsed calculation
+        devices_to_shutdown = []
+
         for dev_id, online in online_status.items():
             dev_info = DEVICES[dev_id]
             state = _load_state()
@@ -307,7 +316,7 @@ def _budget_tick():
 
             # Expired budget + device back online → shut it down
             if current_budget <= 0 and online:
-                dev_info["turnoff"]()
+                devices_to_shutdown.append(dev_id)
                 _set_budget(dev_id, 0.0)
                 continue
 
@@ -320,11 +329,15 @@ def _budget_tick():
                 _set_budget(dev_id, new_budget)
 
                 if new_budget <= 0:
-                    dev_info["turnoff"]()
+                    devices_to_shutdown.append(dev_id)
             else:
                 # Always update last_check even when offline
                 _set_budget(dev_id, current_budget)
 
+        # Shutdown all devices that hit zero budget in parallel
+        if devices_to_shutdown:
+            _shutdown_devices(devices_to_shutdown)
+
 
 def start_timer():
     """Start the background budget timer (runs every 10s)."""